In recent years, devices that detect weak light have been widely introduced mainly in the medical and research fields. Such devices mostly use a relatively expensive photomultiplier tube as a detection unit of weak light.
In addition, a device that detects weak light using an image sensor such as a CMOS (Complementary Metal Oxide Semiconductor) image sensor that can be manufactured at a low cost instead of a photomultiplier tube has also been proposed (for example, refer to Patent Literature 1).